There are some that have blanking. MSOX3000T has it but as a logic function, (ON/OFF) not analog.... Still useful for blanking, just not for full analog modulation of trace..
What input does it use to blank and is the threshold variable?
MANUAL:
Z-Axis Input in XY Display Mode (Blanking)
When you select the XY display mode, the time base is turned off. Channel 1 is the X-axis
input, channel 2 is the Y-axis input, and the EXT TRIG IN is the Z-axis input. If you only want to
see portions of the Y versus X display, use the Z-axis input. Z-axis turns the trace on and off
(analog oscilloscopes called this Z-axis blanking because it turned the beam on and off).
When Z is low (<1.4 V), Y versus X is displayed; when Z is high (>1.4 V), the trace is turned off.